Lotus Elan

QED 420 Jetting recommendation

PostPost by: vstibbard » Sat Oct 20, 2012 6:12 am

Hoping someone can suggest a start point for jetting to suit following spec engine I'm assembling for Elan which is primarily to be used for road/rally use

QED 420 with Q55 springs, forged pistons comp ~11.1:1, inlet valves 1.625, exhausts 1.4 with inlet/exhaust ports opened up and cleaned up to match, steel crank, rods and will be using 40MM DCOE carbs.

I'm seeking a starting point for jetting, chokes etc

Regards

V
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PostPost by: holywood3645 » Sat Oct 20, 2012 6:28 am

What cc is you motor? What ignition system is installed and what cam timing have you dialed in?

420S is normally set up for a 7000rpm top end. It sounds like yours could go higher.

James
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PostPost by: ardee_selby » Sat Oct 20, 2012 8:15 am

A quote from QED in this thread: elan-f15/qed-420-cams-t23066.html

"We provide jetting info for Weber and Dellorto 40/45's with the cams, along with the timing figures"

Cheers - Richard
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PostPost by: rgh0 » Sat Oct 20, 2012 8:40 am

Hi Vern

I would be careful about using the Q55 springs above 6500 rpm. Your engine looks like it is intended to rev a lot higher
They are a very soft spring with a relatively low maximum nose load at coil bind. Good for a standard bottom end with the 420 cam but I beleive they may struggle to follow the cam if you push the revs higher than standard.
Have a look at the spring data I posted under the mods section a while back

cheers
Rohan
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PostPost by: mark030358 » Sat Oct 20, 2012 7:39 pm

See below...
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form 1 6.jpeg and
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PostPost by: vstibbard » Sun Oct 21, 2012 10:50 am

Thanks all, capacity is 1594, electronic ignition is being used. Based on the cam specs id not expect it to make power beyond 7000 especially wirh 40's. Limiter will be set to 7200.

Steel bottom wnd really insurance as these engines are getting harder to source quality original parts cranks had lots of work and by time rods are prepared theyre close to cost of steel set, and bank balance does not extend to new head etc if it has a problem.

Rohan have you compared the phase iv BRM cam to McCoy450's? I will be building an engine for my 26R as it currently got the original unit and want to keep it, will go down the McCoy route for it,

Cheers Vaughan
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PostPost by: holywood3645 » Sun Oct 21, 2012 5:42 pm

My Motor was built to the QED SS spec. 1700cc Q420 cams 40s etc.
I used the timing and carb jetting supplied by QED (same as posted here)
The only difference being I opted for stiffer valve springs.
It pulls well from low RPM under load. There is a stumble around 2500 rpm, then goes like a train. I think the jetting could be improved. My CR is10.5

The QED spec provides a lively road car that's a lot of fun to drive.
James

I would like to hear about any revised jetting updates for the 40DCOE's that dial the performance in better.
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PostPost by: bill308 » Mon Oct 22, 2012 1:51 am

I think one has to take into account the type of fuel to be used. In the US, the 10% ethanol mix probably requires a slighly richer jet set.

Bill
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PostPost by: rgh0 » Mon Oct 22, 2012 10:09 am

Hi Vaughan ( sorry for the wrong name before :oops: )

I dont have the BRM phase 4 cam specs handy - do you know them.

In general the older racing cams grinds are too long a duration and too slow in their action compared to a modern cam of the same lift. This gives a big hole in the midrange in trying to get maximum top end power. This can still work ok in a light open wheeler that can also change ratios to suit circuits but the heavier elan with its fixed GB ratios and a more restricted exhaust needs a shorter duration to maintain mid range torque. Modern cam profiles and springs can accomodate a more agressive cam acceleration profile that achieves both top end power and mid range torque.

Using the McCoy 450's on both inlet and exhaust will give around 175hp that is extremely tractable and easy to drive in a 1600 cc Elan with a McCoy race ported head 45DCOEs and a good exhaust such as the TTR competition exhaust and work well to a maximum rev target of around 8000 rpm. These cams are short duration with great mid range torque but start to fall off above about 7500 rpm and no point reving them much beyond 8000 rpm

Using the McCoy 490 grind on the inlet while keeping the 450 on the exhaust works well and lifts the power band to 8500 plus rpm and another 5 to 10 hp at peak without much loss in midrange torque, you can target using 9000 rpm with this set up. Using the McCoy 490 on inlet and exhaust may give a little more power again but you need a rev target above 9000rpm and the loss in midrange torque gives you slower lap times in real life from the tests done in a group S Seven I have been part of.

cheers
Rohan
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PostPost by: vstibbard » Tue Oct 23, 2012 9:17 am

Thanks Rohan, appreciate the comments re the various McCoy cam, im not keen to build a high rev engine due to service life, prefer more torque and work on driving it well, the 26R will be out at Tasman but only for the parade laps as will not have chance to test prior tomthe meeting.

Be good to meet up some time, im hoping subject to work to do Philip Is nd Lakeside next year, but will run the original engine until then.

Cheers V
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